The present invention relates to processes for etching aluminum from a substrate.
Reactive ion etching processes are used in the fabrication of semiconductor and other devices with submicron sized features, such as integrated circuit chips. These processes are used to etch aluminum alloys from a surface of a silicon wafer, where portions of the aluminum are protected by a pattern of an etch-resistant "resist" material, such as photoresist or oxide-hardmask. The protected aluminum portions form "features" which are left on the silicon wafer to form part of the integrated circuits being processed on the wafer. Etching is effected by introducing a process gas into a chamber, generating a plasma in the chamber to create an etch-gas that etches aluminum from the substrate to create a volatile aluminum-containing compound, such as AlCl.sub.3, and removing the volatile aluminum-containing compound from the chamber.
Typically, the process gas comprises BCl.sub.3 and Cl.sub.2, and optionally N.sub.2. A problem with this process gas is that relatively thick residues or deposits containing Al, Cl, B and N, form on the chamber walls and on the resist material. The deposit on the chamber walls can form particles that contaminate the wafers. Further, the resist material can have excessive amounts of residue form on it, thereby undesirably increasing the area protected by the resist material. These problems can render the processed wafer unsuitable for use.
A deposit layer can also form on the sidewalls of the freshly etched channels in the aluminum containing layer. This deposit layer serves as a "passivating" barrier which hinders continued etching, thereby preventing "isotropic" etching or undercutting. Isotropic etching occurs when etching proceeds horizontally below the resist layer, instead of vertically through the uncoated portions, resulting in the lower portions of the features being inwardly sloped. Although vertical "anisotropic" etching is desirable, an excessive passivating layer on the sidewalls is difficult to subsequently clean-off. With typical BCl.sub.3 based systems, it is difficult to control the amount of deposit on the sidewalls.
Furthermore, typical BCl.sub.3 based systems result in increased profile microloading, which occurs when the cross-sectional profile of the features formed in the aluminum containing layer vary as a function of the spacing between the features. It is desirable to have an etching process which provides features with a uniform cross-section regardless of the spacing between the features.
It is also desirable to obtain high etch rates and a high aluminum to resist etching selectivity ratio for process efficacy.
Accordingly, there is a need for a process for etching aluminum-containing materials which minimizes contamination of the chamber and the substrate, which is substantially only anisotropic, which does not result in formation of oversized features, which provides reduced profile microloading, and which does not form excessive deposit on the sidewalls of the etched channels. It is also desirable to obtain high etch rates and a high aluminum to resist selectivity ratio.